Checking for cracks

[Drew Hause]

More than you probably want to know about Magnetic Particle Inspection (MPI)
https://www.nde-ed.org/EducationReso...principles.htm

VERY few testing labs have experience with pattern welded tubes, and interpretation of esp. Twist barrels can be difficult. A normal exam however would be reassuring





MPI is generally considered to be the best method for the detection of fine, shallow surface cracks in iron and steel, especially fatigue cracks. However, defects deeper in the material ie inclusions, may be missed.

It of course tells you nothing about the bore, and for that reason direct observation with a bore scope, and wall thickness measurements of any vintage barrel are needed prior to use.

[Double Trouble]

Drew:

In the attached pictures - the top one: is the bright green line on the "top" barrel a crack ? Likewise, on the bottom picture, are the two bright green lines cracks (with the fine lines merely being normal features of twist barrels) ?

[Drew Hause]

John: here is that barrel segment



and radiography of the segment showed no evidence of cracks. The 2 markers are the ? indicators on MPI. The small lucent areas are felt to be bore pits